1. Field of the Invention
The present invention relates to conversion of orifice fittings.
2. Description of the Prior Art
Orifice plates have been used in pipelines carrying gas or liquid to form pressure differentials for metering purposes. In addition to orifice flanges, two types of orifice fittings have been used to mount these orifice plates in a pipeline.
A first type of orifice fitting, known as a "senior" fitting, had two compartments or chambers separated by a valve mounted in the orifice fitting. A first one of the compartments held the orifice plate in a position for use in the pipeline. When it became desirable to inspect, repair, replace or otherwise service the orifice plate, the valve was opened and the plate moved therethrough to the second compartment. The valve was then again closed, so that the second compartment could be opened and the orifice plate serviced while pressure was maintained in the pipeline by the valve in the "senior" fitting. Examples of this type fitting are disclosed in U.S. Pat. Nos. 1,569,305; 1,965,826; 2,014,682; 2,050,544; 2,688,987. There were also several special constructions or types of "senior" fittings, such as those in U.S. Pat. Nos. 2,896,688 and 2,964,063.
A second orifice fitting, commonly known in the art as a "simplex," "semi" or "junior" fitting had no valve and only a single orifice chamber, in which the orifice plate was mounted in place in the pipeline. In order to remove the orifice plate from this type of fitting, pressure in the pipeline had first to be abated, a costly, time-consuming operation during which product was lost from the line. Numerous of these "junior" fittings have been installed in pipelines, and although these fittings are not as desirable as the "senior" fittings for reasons of ecology or economy, the cost of removing them from the pipeline and replacing them with "senior" fittings has limited their replacement.